Cantilevered Planing Platform

Planing or sanding case or drawer sides works best when the
surface being smoothed is fully supported on its underside. The easiest way to
provide the support is to clamp a cantilevered board or panel to your
workbench. For heavy cases, use a stout board. For most drawers, a 3⁄4"-thick scrap plywood panel works fine.
You can secure the work to the platform with clamps, removing them when they
get in the way, or you can size the support panel for a tight fit in the unit
opening, in which case you often don’t need clamps.